To anyone who has been following Valve Software's viral marketing campaign inside Portal--comprehensively chronicled by Bit-Tech--the announcement of Portal 2 should come as no surprise. Today, the suburban Seattle studio made it official: The sequel will arrive this holiday for the PC via the company's Steam service and (presumably) as a boxed retail product.

[UPDATE] Valve has now confirmed the game is coming to the Xbox 360 as well.

There are more portals where that came from.

The original Portal drew high critical praise for its mind-bending style of gameplay, which had players traverse inter-dimensional openings on ceilings, walls, and floors to navigate a deadly research facility. And despite winning 70 accolades, including top honors at the 2008 Game Developers Choice Awards, the game was only three to four hours long. Not so for the sequel, apparently. GameStop-owned magazine Game Informer reports the game will be "a full-fledged, standalone" sequel with "new gameplay mechanics, storyline, and some surprising new twists."

[UPDATE] Though Valve's announcement was minimal, GameStop's Portal 2 product page briefly listed the game as having "single and multiplayer co-op modes." Now, it only has the following short description of the game:

Portal 2 introduces a cast of dynamic new characters, a host of fresh puzzle elements, and a much larger set of devious test chambers. Players will explore never-before-seen areas of the Aperture Science Labs and be reunited with GLaDOS, the occasionally murderous computer companion who guided them through the original game.

Though no story details are known about the sequel, Valve is apparently continuing its viral marketing campaign with yet another brainteaser. Several letters of the announcement were underlined, spelling out the nonsensical word "drattmannh0nee." Possible--but improbable--anagrams include "dethr0ne ant man" and "man the dr0ne."

Portal was first released as a pack-in inside the 2007 Orange Box compilation, which also included Half-Life 2, Half-Life 2: Episodes One and Two, and Team Fortress 2 on PC, 360, and PlayStation 3. (It was also released as stand-alone game for the PC.)